Human in vitro fertilization (IVF) and embryo transfer (ET) was first successfully performed in 1978 and has since been widely practiced to treat infertile couples who have failed with other conventional methods. The IVF/ET procedure typically involves hormonal stimulation of the female to initially suppress her natural ovulation, and then stimulate development of ovarian follicles with fertility drugs. The mature eggs are harvested from the ovary using a needle and then sorted by maturity and egg quality. Preferred eggs are then mixed with sperm from the male to be fertilized. After some time, the embryo(s) mature and are transferred, along with a volume of fluid, to the uterus using a delivery catheter. The delivery catheter is made of soft plastic material to avoid damage to the endometrium of the uterus. The delivery catheter is guided through the cervix to the uterus by a physician where the loaded embryos within the fluid is deposited, completing the ET.
One method of catheter loading is referred to as “the transfer bubble method” and has been universally accepted by professionals and has been in place over four decades. The catheter is loaded with a series of alternate air and transfer liquid (e.g., saline, P-1 or glycerine) in volumes approximating 3 microliters. Volumes of air separate the transfer liquid to keep the embryos contained within the fluid and also to ease visualization of the components. Upon ejection of the fluids, about 100 microliters of air is also ejected with the quantity of medium and transfer liquid containing the embryos. Generally, there are a total of approximately 6 microliters of fluid and 100 microliters of air deposited at the ejection site in the uterus. These volumes can vary greatly depending on specific hospital protocol and there has been research done to study the effects of varying medium volumes upon pregnancy rates. Some studies demonstrate that a transferred volume of less than 50 microliters is optimal for successful ET whereby other studies show that widely varying transfer volumes of medium have little effect on the outcome of IVF procedures.
Studies also have found that the transferred air within the uterus can sometimes act as a barrier that prohibits movement of the embryos from the site of ejection to the optimal location for implantation within the uterus. This air bubble creates an area of surface tension to which the embryos may adhere and remain positioned, prohibiting interaction of the embryo with the receptive surface of the uterus. Moreover, under the transfer bubble method, latent embryos can attach themselves to the internal walls of the catheter requiring further manipulation of the embryos and thereby decreasing the likelihood of successful ET.
While improvements in the techniques and instrumentation used in this procedure have provided significant increases in pregnancy rates and births, the overall numbers remain fairly low, around 25%. There are several factors that impact on IVF success including the design of the delivery catheter. Ultrasound guided catheters have been included in ET procedures to aid visualization of the tip and facilitate optimized embryo deposition at the prime location within the uterus.
In addition, the high cost of the IVF procedure combined with this low probability of success compels couples to deliver multiple embryos to increase the chance of at least one successful implantation. Often, unwanted multiple births result and jeopardize the health of mother and/or children, which has recently raised questions concerning the medical ethics of such practice. If a higher pregnancy rate could be achieved, the need for multiple embryo delivery would be lessened or possibly eliminated.
With the high cost of IVF and contrastingly low pregnancy rate, what is needed is a method of ET that reduces the quantity of air that is typically transferred to the uterus along with the embryos in medium. The conventional method of catheter loading referred to as “the transfer bubble method” that deposits these relatively large volumes of air has been taught worldwide and universally accepted by professionals in the IVF field. Even as studies demonstrate the difficulties associated with this large transferred air bubble, this method is the only one used. An improved method of ET that eliminates any volume of transferred air will undoubtedly improve the probability of successful embryo implantation and increase pregnancy rates overall.